Several viruses also cause foodborne illness. Viruses differ from bacteria in that they are smaller, require a living animal or human host to grow and reproduce, do not multiply in foods and are not complete cells. Viruses are very small microorganisms, ranging in size from 0.02 to 0.4 micrometers in diameter, whereas bacteria generally range in size from 0.5 to 5 micrometers.
Ingestion of only a few viral particles is enough to produce an infection. The viruses most frequently involved in foodborne infections are human Norovirus (NoV) and hepatitis A virus (HAV), but other viruses such as Enterovirus (EV), human Rotavirus (HRV), hepatitis E virus (HEV), astrovirus (AstV), Aichi virus (AiV), Sapovirus, Coronavirus, Parvovirus, and human adenovirus (HAdV) can also be transmitted by food.
In contrast to bacteria, which are free living, viruses use the host cells to replicate. Humans are host to a number of viruses that to reproduce in the intestines and then are excreted in the feces. Thus, transmission of viruses comes from contact with sewerage or water contaminated by fecal matter or direct contact with human fecal material.
Foods at greatest risk of virus contamination at the preharvest stage are shellfish, soft berry fruits, herbs, and salad vegetables. Raw or uncooked molluscan shellfish (oyster, clams, mussels and scallops) are the food most often associated with foodborne viral diseases.
The majority of outbreaks have followed the consumption of raw oysters, although cooked oysters have also been implicated. The short shelf life of oysters has resulted to the fact that most shellfish-borne outbreaks have occurred locally.
Human pathogenic viruses are often discharge into marine waters through treated and untreated sewage. As shellfish filter contaminants from these polluted waters, they store them within their edible tissues.
Shellfish grown and harvested from polluted waters have been implicated in outbreaks of viral diseases. The other main source of transmission is from infected food workers who have poor personal hygiene.
Therefore, proper hand washing and using a clean water supply are vital to controlling the spread of foodborne viruses.
Virus contamination in food
